Crystallization of silver halide within an aqueous mixture of a water soluble silver complex and a polymeric colloid binder

ABSTRACT

Silver halide emulsion layers are formed by mixing a watersoluble silver halide complex and a polymeric binder material, casting a layer of said material and crystallizing silver halide grains therein.

[451 May 13, 1975 CRYSTALLIZATION OF SILVER IIALIDE WITHIN AN AQUEOUS MIXTURE OF A {56] References Cited UNITED STATES PATENTS WATER SOLUBLE SILVER COMPLEX AND A POLYMERIC COLLOID BINDER 3,600,175 8/1971 Anderson et al. 96/65 [75] Inventor: Vivian K. Walworth, Concord,

Mass.

Primary ExaminerNorman G. Torchin Assistant ExaminerAlfonso T. Suro Pico Attorney, Agent, or Firm-Philip G. Kiely; Robert M. Ford [73] Assignee: Polaroid Corporation, Cambridge,

Mass.

[22] Filed: July 27, 1973 [57] ABSTRACT Silver halide emulsion layers are formed by mixing a [21] Appl. No.: 383,106

[52] US. 96/114; 96/94 R; 96/107; water-soluble silver halide complex and a polymeric 9 1 7 binder material G030 1/18 casting a layer of said material and G03c 1/02 Field of Search......

; 03 1/0 crystallizing silver halide grains therein.

[51] Int. Cl.

H4 18 Claims, 1 Drawing Figure CRYSTALLIZATION OF SILVER I-IALIDE WITHIN AN AQUEOUS MIXTURE OF A WATER SOLUBLE SILVER COMPLEX AND A POLYMERIC COLLOID BINDER BACKGROUND OF THE INVENTION Copending application Ser. No. 3l I ,690, filed Dec. 4, l972, teaches that silver halide photographic emulsions can be prepared by forming a water-soluble silver halide complex such as, for example, AgCl AgClf AgBr AgBrf", AgBrJ, Ag Br Agl Aglf', AgCl Br Ag l and AgClBr complexes. and breaking the complexes as by dilution, preferably in the absence of a binder material. The thusformed insoluble silver halide crystals are collected, disposed in a binder material and coated on a support. Chemical and spectral sensitization of the grains may be carried out before the crystals are disposed in a binder to obtain more efficient sensitization.

My copending application Ser. No. 383,262 filed concurrently herewith teaches the formation of photographic silver halide emulsion layers by applying a watersoluble silver halide complex of the character described above to a gelled substrate and decomplexing to form silver halide grains in situ in the layer. This procedure permits crystal growth but prevents agglomeration of the crystals which are held substantially immobile in the binder matrix.

The above-described copending applications are incorporated herein in their entirety by reference.

SUMMARY OF THE INVENTION Silver halide emulsion layers are formed by mixing a watersoluble silver halide complex with a polymeric binder material, casting a layer of said mixture and breaking the complex to form silver halide crystals in the layer. Decomplexation is preferably achieved by treating the layer with a material to break the complex, for example, contacting the layer with sufficient water to accomplish decomplexation by dilution. The term water-soluble silver halide complex" as used herein is intended to refer to mixtures of two or more complexes as well as a single complex.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a photomicrograph of silver halide crystals formed by the novel processes of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention involves the formation ofsilver halide crystals from an inorganic, water-soluble silver halide complex in a polymeric binder layer or substrate. As stated above, such water-soluble silver halide complexes are known to the art. In contrast to grains of conventional emulsions, the grains of the present invention are not the product of the precipitation of a water-soluble silver salt by a water-soluble halide. In other words, halides are not employed as the precipitant in the present invention. Such conventional proce dures are generally carried out in the presence ofa substantial amount of colloid binder material to provide an environment which permits the growth of the crystals to the desired size and prevents agglomeration of crystals during the growth process.

In the present invention, a fluid comprising a solution ofa silver halide complex and a polymeric binder material is formed and a layer of the mixture is cast and allowed to set. Decomplexation of the water-soluble complex is then carried out, forming silver halide crystals in the layers. There is thus produced a layer of sil ver halide crystals of substantially uniform size and uniformly distributed throughout with respect to area of said layer. The uniformity of distribution of crystals is achieved by the initial mixing step and the complex concentration depletion which is uniform with respect to area of the layer.

The decomplexation of the silver halide complex is accomplished by dilution, i.e., by contacting the cast layer with a diluting medium, preferably water. The specific degree of dilution is not critical; it is only nec essary to dilute sufficiently to provide decomplexation and precipitation. Insoluble silver halide crystals will be formed in the layer and held immobile in the binder. The speed with which crystal formation occurs depends upon permeability and other properties of the binder layer.

Having carried out the steps necessary to provide the precipitate, separation of excess salts is relatively easy. By washing the layer with water, the undesirable soluble materials are removed without affecting the silver halide crystals and substrate in which they are retained. The crystals may then be given any optional treatments desired such as that described below, thereby providing a photographic silver halide emulsion layer in a relatively short time and with a minimum of equipment and processing steps.

The novel process of the present invention is preferably carried out by forming a water-soluble complex of silver wherein the anion is chloride, bromide or iodide. For example, silver nitrate may be reacted with potassium bromide and/or calcium bromide to form silver bromide. Silver bromide solid is also commercially obtainable. The silver bromide is then added to a solution ofa soluble bromide such as calcium bromide, lithium bromide or potassium bromide to produce a silver bromide complex. The solution of the complex is preferably a saturated solution, but it is not critical that it be saturated. The thus-formed soluble complex is mixed with the desired binder material and a layer is cast and allowed to set. Upon contact with a diluting medium such as water, the relatively rapid change in the concentration results in breaking the complex, forming water-insoluble silver halide crystals which precipitate in the set binder layer. The excess complex salts which remain soluble are easily removed by washing. If desired, the emulsion may be chemically or spectrally sensitized. Chemical and spectral sensitizers may be added to the initial coating solution or to the layer with the diluting medium or subsequent to crystal formation.

The halide salts which remain in solution subsequent to decomplexation can be recycled for use in forming new watersoluble silver halide complex. Thus, very little waste of materials is involved providing ecological and economic advantages to the process of the present invention.

While dilution is the preferred method of decomplexation, it should be understood that other conventional methods of crystallization may be employed, such as temperature change, evaporation and nucleation and combinations of such conditions.

In a particularly preferred embodiment, the complex solution is formed at elevated temperatures to provide optimum solubility of the complex. The dilution is then carried out at a lower temperature to provide enhanced yield of silver halide precipitate.

By means of the present invention, a variety of crystal sizes may be produced. In a preferred embodiment, the system is free of particulate material; however, in order to hasten the precipitation, which will result in finer crystals, it may be desirable to provide nucleating material. The nucleating material may comprise substantially any particulate material, that is, an insoluble substance of a size smaller than the desired grain size. The specific material chosen is not critical. As examples of a suitable particulate nucleating material, mention may be made of gold sulfide, colloidal gold, silver iodide, colloidal silver, and colloidal silver bromide.

In the preferred embodiment, a halide salt is added to the diluting medium, thereby modulating the rapidity with which the complex is broken and crystal formation occurs. If the halide in the diluting medium is the same as the halide in the complex, crystal formation will be slowed, resulting in relatively large grain formation. If a halide other than the halide in the complex is employed in the diluting medium and provided that the halide in the diluting medium forms a less soluble silver halide than the halide of the complex, precipitation and crystal formation are accelerated, resulting in smaller silver halide crystals. In this situation, the breaking of the complex will be relatively rapid and complete, with the formation of a core of silver halide rich in the halide employed in the diluting medium. The less soluble silver halide (halide of diluting medium) functions as a nucleus around which silver halide crystal (halide of the complex) forms. It should be understood that a combination of different halides at different ratios may be used in the diluting medium.

In employing a salt of a halide in the diluting medium, it has been found that a wide variety of cations may be employed. As examples of suitable cations, mention may be made of potassium, lithium, sodium, rubidium, calcium, strontium, barium and ammonium. In addition to performing the desired modulation effect on the crystallization process, it has also been found that the employment of the aforementioned cations does not interfere with the photographic performance of the emulsion prepared from the silver halide crystals formed in the process of the present invention.

It has also been found that various organic solvents which are miscible with water may be employed in the diluting medium in order to provide various modifications to the silver halide crystal. As examples of solvents which may be employed, mention may be made of dimethyl sulfoxide, ethanol, 2-methoxy ethanol, acetone and dimethyl formamide.

Silver halide crystal growth may be modified by compounds which adsorb preferentially to specific faces of the crystal (see, for example, F. L. Claes et al, Journal of Phomgraplzic Science, Vol. 2l, I973, pages 3950).

The photographic silver halide emulsion layer of the present invention may be treated with a variety of materials. For example, various materials known to the art may be incorporated therein such as hardeners, buf fers, dye developers, antifoggants, stabilizers, and other reagents conventionally disposed in silver halide emulsions. Sensitization may be carried out by dissolving chemical or spectral sensitizers in the substrate or by bathing after formation of the layer and contained crystals. Surfactants and humectants may also be advantageously employed.

In a particularly preferred embodiment, the complex solution is formed at elevated temperatures to provide optimum solubility of the complex. The application of the complex solution is carried out a lower temperature to provide enhanced yield of silver halide precipitate.

It will be noted that the makeup of the diluting medium can be modified by the addition of combinations of the aforementioned materials at varying concentrations in order to achieve a silver halide crystal of predetermined size and shape as well as composition, since the halide ratios of crystals have a known effect on sensitivity and other properties.

Any natural or synthetic polymeric material may be employed in the silver halide emulsion preparation of the present invention. Preferably, gelatin is employed.

Other suitable binder colloids include natural and/or synthetic polymeric material such as albumin; casein; or min; or resins such as a cellulose derivative, as described in U.S. Pat. Nos. 2,322,085 and 2,541,474; vinyl polymers such as described in U.S. Pat. Nos.

2,253,078; 2,276,322; 2,276,323; 2,281,703; 2,310,223; 2,3ll,058; 2,311,059; 2,414,208; 2,461,023; 2,484,456; 2,538,257; 2,579,016; 2,6l4,93l; 2,624,674; 2,632,704; 2,642,420;

2,678,884; 2,691,582; 2,725,296; 2,753,264; and the like.

While not intending to be bound by theory, it is believed that the mixing of the water-soluble complex and the binder material prevents any substantial crystallization, since the binder constitutes a crystal growth inhibiting medium. Thus, a relatively stable mixture of binder and complex can be formed and processed in a variety of ways without substantial crystallization until contacted with a diluting medium. It is only necessary to avoid introducing excessive diluting conditions into the mixture prior to the time crystal formation is desired.

By means of the present invention, silver halide emul' sion layers can be continuously and rapidly formed and incorporated into film units. For example, the watersoluble silver halide complex and binder may be premixed and applied to a suitable carrier or support as the support is moved past a coating station. After drying the thus-formed layer and/or gelling or setting the binder, crystallization may be initiated by passing the layer through a water bath. The water will permeate the layer forming the silver halide grains as described above. The layer may then be washed to remove any excess reagents or by-products, treated with chemical or spectral sensitizers, further treated with conventional hardeners and then incorporated into a film unit, either with the support or optionally after removal of the support. It will be seen, therefore, that a relatively rapid, simple and continuous process employing a minimum of materials and equipment can produce silver halide emulsions.

The following nonlimiting examples illustrate the preparation of emulsions within the scope of the present invention. In the following examples, the saturated silver halide complex solution was prepared by solubilizing silver bromide with a soluble bromide, i.e., by adding potassium, calcium or lithium bromide and silver bromide solids to water at room temperature until the halides no longer dissolve to provide a solution of about 8N to l0N bromide and about 0.3N to 0.5N silver.

EXAMPLE I A saturated silver bromide solution was prepared by adding 1400 g. of lithium bromide to 650 ml. of water and cooling and to this solution was added 85 g. of silver nitrate and 100 ml. of water. The resulting mixture was colled to room temperature and allowed to equilibrate for 2 hours. The supernatant liquid was decanted and filtered. 100 ml. of the filtered solution was added to g. of dry gelatin and mixed thoroughly at 40 C. A layer of the mixture was coated over a polyester sup port and allowed to set for 5 minutes at room temperature. The layer was then dipped into distilled water and dried with forced hot air. Uniform silver halide grains about 0.7 microns in diameter were found. The thusformed film unit was exposed to blue light through a step wedge with one-half stop increments and processed with Type 107 receiving sheet and processing composition (Polaroid Corportion, Cambridge, Mass. by diffusion transfer processing. Observation of the resulting positive image indicated that a light sensitive photograpahic emulsion layer of relatively low speed had been produced.

EXAMPLE II A film unit was prepared by coating a 1% solution of an anionic heteropolysaccharide thickener (available from General Mills, lnc.,Kankakee, lll., under the trade name Xanthan Gum XB23) on triacetate film base at a coverage of about 1.7 gift". After the first layer was dry a mixture of 0.5 g. of Irish moss extract (available from S. B. Penick & Co., New York, N.Y., under the trade name PENCOGEL) and 50 ml. of silver halide complex as described in Example I above was coated over it at a coverage of 6.4 g./ft. The thus-formed layered structure was dipped into a 10% potassium iodide solution for 10 seconds, washed with distilled water to remove all salts and excess reagents and then dried. Silver halide crystals about 0.1 to 0.4 microns were formed. Silver Coverage was about 158 mg/ft. Exposure and photographic processing with Type 42 receiv ing sheet and processing composition (Polaroid Corporation, Cambridge, Mass.) showed that a light sensitive photographic emulsion layer had been produced which yielded a positive image.

EXAMPLE III A mixture of 50 ml. of silver halide complex as prepared in Example I and 0.25 g.of Xanthan Gum XB23 was prepared and coated over triacetate film base at a coverage of 3.0 g./ft. The layer was dipped into distilled water and dried. A 0.1 percent aqueous solution of a sensitizing dye of the formula:

was coated over the layer at a coverage of 3.0 mljft Exposure and photographic processing with Type 42 receiving sheet and processing composition showed a positive image of moderate density. Spectral sensitivity to 650 nm was observed.

EXAMPLE IV A plastic film base was coated, in order, with nonionic liquid alkyloamide wetting agent (available under the trade name Solar Fl83 from Swift & Company, Chicago, Ill.), a 50-50 by weight mixture of silver halide complex (as described in Example I) and 20% (by weight) gelatin and a saturated solution of lithium bromide and potassium iodide in gelatin. All layers were coated at a coverage of 3.0 g./ft. and the film structure partially dried between coatings. After formation of all the layers, the structure was washed with distilled water and dried. An examination of the layer showed formation and growth of substantially uniform grains of approximately l micron in diameter. The FIGURE is a photomicrograph at a magnification of about 3460X, of grains prepared according to the procedure of Example IV.

The order of addition of the binder and complex is not critical; any order of addition may be employed.

By means of the novel processes ofthe present invcn tion, layers containing as much as 200 mg./ft. silver can be prepared satisfactorily.

The silver halide crystals prepared by the present invention may be chemically sensitized by conventional chemical sensitizers known to the art, e.g., gold or noble metal sensitization, sulfur sensitization, such as by a labile sulfur compound, and reduction sensitization, i.e., treatment of the silver halide with a strong reducing agent. With regard to the use of chemical sensitizing agents, mention may be made of U.S. Pat. Nos. 1,574,944; 1,623,499; and 2,410,689.

The silver halide grains can also be treated with salts of the noble metals, such as ruthenium, rhodium, palladium iridium and platinum. Representative compounds are ammonium chloropalladate, potassium chloroplatinate, and sodium chloropalladite, as described in U.S. Pat. Nos. 2,448,060; 2,566,245; and 2,566,263.

The silver halide grains can also be chemically sensitized with gold salts as described in U.S. Pat. Nos. 2,399,083 and 2,642,361. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2- aurosulfobenzothiazole methochloride.

The silver halide grains can also be reduction sensitized with reducing agents, such as stannous salts as described in U.S. Pat. No. 2,487,850, polyamines, such as diethylcne triamine as described in U.S. Pat. No. 2,518,698, polyamines, such as spermine as described in U.S. Pat. No. 2,521,925 or bis-(B-aminoethyl) sulfide and its water-soluble salts as described in U.S. PAT. No. 2,521,926.

Sensitizers of the solid semiconductor type, such as lead oxide, may also be employed. Such sensitizers are disclosed and claimed in copending U.S. applications Ser. Nos. 341,707 and 341,708, both filed Mar. 15,

The chemical sensitizers employed may be predisposed in the substrate prior to the crystal formation; in the soluble complex solution, in the diluting medium or in a subsequent solution for application to the grains.

Spectral sensitization of the silver halide crystals may be accomplished as described above by contact of the crystal composition with an effective concentration of the selected spectral sensitizing dyes dissolved in an appropriate dispersing solvent such as methanol, ethanol, acetone, water and the like; all according to the traditional procedures of the art, as described in Hamer, F. M., The Cyanine Dyes and Related Compounds.

Additional optional additives, such as coating aids, hardeners. viscositydncreasing agents, stabilizers, preservatives, and the like, also may be incorporated in the emulsion formulation prior to and/or subsequent to the formation of the grains. Material for promoting adhesion between the layers may also be employed.

While the emulsion layers of the present invention have been described primarily in terms of use in diffusion transfer processes, it should be understood that the layers may be utilized in other types of photographic processing and film units, such as those employed in conventional art development, including direct positive and direct negetive, reversal processing, and the like.

What is claimed is:

l. A method for forming a photographic silver halide emulsion layer which comprises mixing an aqueous solution of a water-soluble complex of silver halide complexed by excess halide and a polymeric binder material. forming a layer of said mixture and crystallizing photosensitive silver halide grains in said layer by decomplexation.

2. A method as defined in claim 1 wherein said solution of water-soluble complex is saturated.

3. A method as defined in claim 1 wherein said polymeric binder material is a natural material.

4. A method as defined in claim 3 wherein said binder material is gelatin.

5. A method as defined in claim 1 wherein said polymeric binder material is a synthetic polymeric material.

6. A method as defined in claim 1 wherein said layer is at least partially dried prior to decomplexation.

7. A method as defined in claim 1 wherein said decomplexation is accomplished by dilution with an aqueous solution.

8. A method as defined in claim 7 wherein the diluting medium is water.

9. A method as defined in claim 8 wherein the diluting medium includes an agent for modulating the crystallization of the silver halide.

10. A method as defined in claim 9 wherein said agent is a watensoluble halide salt.

11. A method as defined in claim 10 wherein said water-soluble halide salt comprises the same halide as the halide of the water-soluble complex.

12. A method as defined in claim 1 wherein said complex is a saturated silver bromide complex.

13. A method as defined in claim 1 which includes the step of washing said layer subsequent to crystallization.

14. A method as defined in claim 7 wherein said diluting medium includes a photographic sensitizing agent.

15. A method as defined in claim 14 wherein said sensitizing agent is a chemical sensitizer.

16. A method as defined in claim 14 wherein said sensitizing agent is a spectral sensitizer.

17. A method as defined in claim 1 wherein a photographic sensitizing agent is applied to said layer subsequent to crystal formation.

18. A method as defined in claim 1 wherein said solution includes a photographic sensitizing agent. 

1. A METHOD FOR FORMING A PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER WHICH COMPRISES MIXING AN AQUEOUS SOLUTION OF A WATER-SOLUBLE COMPLEX OF SILVER HALIDE COMPLEXED BY EXCESS HALIDE AND A POLYMERIC BINDER MATEIAL, FORMING A LAYER OF SAID MIXTURE AND CRYSTALLIZING PHOTOSENSITIVE SLIVER HALIDE GRAINS IN SAID LAYER BY DECOMPLEXATION.
 2. A method as defined in claim 1 wherein said solution of water-soluble complex is saturated.
 3. A method as defined in claim 1 wherein said polymeric binder material is a natural material.
 4. A method as defined in claim 3 wherein said binder material is gelatin.
 5. A method as defined in claim 1 wherein said polymeric binder material is a synthetic polymeric material.
 6. A method as defined in claim 1 wherein said layer is at least partially dried prior to decomplexation.
 7. A method as defined in claim 1 wherein said decomplexation is accomplished by dilution with an aqueous solution.
 8. A method as defined in claim 7 wherein the diluting medium is water.
 9. A method as defined in claim 8 wherein the diluting medium includes an agent for modulating the crystallization of the silver halide.
 10. A method as defined in claim 9 wherein said agent is a water-soluble halide salt.
 11. A method as defined in claim 10 wherein said water-soluble halide salt comprises the same halide as the halide of the water-soluble complex.
 12. A method as defined in claim 1 wherein said complex is a saturated silver bromide complex.
 13. A method as defined in claim 1 which includes the step of washing said layer subsequent to crystallization.
 14. A method as defined in claim 7 wherein said diluting medium includes a photographic sensitizing agent.
 15. A method as defined in claim 14 wherein said sensitizing agent is a chemical sensitizer.
 16. A method as defined in claim 14 wherein said sensitizing agent is a spectral sensitizer.
 17. A method as defined in claim 1 wherein a photographic sensitizing agent is applied to said layer subsequent to crystal formation.
 18. A method as defined in claim 1 wherein said solution includes a photographic sensitizing agent. 